Flotation apparatus and processes respond to changing conditions resulting from depletion of high grade material sources, such as coal, along with a rising demand for the material. Also, rising cost factors have increased attempts to expand the production ability of the flotation apparatus. Another problem area is fine particle processing for known apparatus which has not been particularly suitable for this purpose. It has been suggested that air bubble formation at the impeller is at the point at which hydrophobic particles apparently attach to the bubbles in that region. The production of air bubbles has been thought of as a process of forcing a division of large bubbles into smaller bubbles. It has also been considered that in the generation of fine air bubbles the addition of reagents is more important than distribution and that velocity of the distributor may also be regarded as a prime cause of the production of fine air bubbles or at least an important cause of fine air bubbles.
In a state of the art article, published in the Minerals Science Engineering Vol. 9, No. 3, July 1977, it is stated "Good mixing promotes particle-bubble contact and thus particle-bubble adhesion. Too much mixing, however, would detach particles from the air bubbles. If the degree of mixing were too low the particles would not have the kinetic energy required to attach to the air bubbles. Thus the degree of mixing in the pulp is important." In the same article, as a conclusion, it is stated "It is likely that improved productivity of flotation cells handling very fine particles could come about by using bubbles that are smaller than those customarily produced in flotation machines. There is clearly a need to be able to make bubbles in the range of 100 to 500 um in diameter in a simple controllable way, these sizes being beyond the capabilities of conventional turbine agitators and air diffusers."
It has been found that in the removal of the desirable materials from a slurry it is important to produce a mass of fine air bubbles with extremely low rotational speed of the distributor. It has also been found that important benefits are obtained if sanding in the area of the distributor is minimized so that the sanding condition cannot interfere with bubble production. Prior apparatuses of the flotation type have had some serious disadvantages. For example, prior apparatuses of relatively good efficiency have been complicated in construction which resulted in higher cost both in assembly and in the disassembly for maintenance purposes. Known flotation cell mechanisms utilize excessive agitation which is similar to the action experienced in a pump. This type of mixing greatly increases the probability of refuse entrapment which is of course detrimental to high yields required in present day flotation cells. Also, known apparatuses require higher power input, thereby further increasing the operating cost of the cells. On the other hand, apparatuses of simpler construction have not been efficient, thereby increasing production cost and requiring the installation of more units for a given production requirement.